Fair Test
There are factors that need to be taken in to account when I collect my results, they are:-
Human error - Results could be read wrongly.
Temperature – If the temperature is higher then the reaction will be speeded up.
Size of marble chips - The marble chips might be different sizes and have different surface areas, which will affect the rate of reaction.
Acid - The acid used must be the same because different acids may have different types of reaction with the marble chips.
Time – More time means there is more time for the reaction to take place.
Prediction
I predict that the stronger the concentration of acid the more gas there will be. This is because when the acid is stronger a bigger reaction will take place therefore more gas will be released; this is because there are more acid molecules to react with the marble chips. When the acid is poured on the marble chips it begins to react with the marble and the atoms are released in gas form. So when the acid is stronger the faster the molecules will react and the more atoms will be released making more gas.
Apparatus
- 25ml Measuring Cylinder
- 200ml Measuring Cylinder
- Conical Flask
- Tube and Bung
- Marble Chips (about same size)
- Water Basin
- Stop Clock
Diagram
Method
Half fill a basin with water and get the correct concentration of acid and water ready in a 25ml measuring cylinder. The amount used should be 25ml for 100% concentration and 5ml for 20% etc. Then 4 grams of marble chips should be weighed in a conical flask. A 200ml measuring cylinder should be filled with water and then turned upside down and sat in the water basin without losing any water. A tube attached to a bung should be slotted in to the water basin and up into the measuring cylinder. The acid should be poured into the conical flask with the marble chips and a stop clock should be started at the same time that the bung is fitted on top of the conical flask. Gas may be given off and collected by the measuring cylinder. Every 10 seconds for 60 seconds the amount of gas should be recorded. This should be repeated to make sure the results were accurate and then this should be done for 5 other concentrations of acid.
Concentrated acid will be used, so at all times it is important to be careful and to always wear goggles. Any spillages on to hands should be washed off immediately.
I will be doing six different concentrations of acid and two repeated readings for each to make sure I get accurate results and to make sure my results clearly show how the concentration of acid affects the reaction rate with marble chips.
Preliminary
I tested with the 250ml measuring tube because it is the largest measuring tube and I also used the strongest concentration of acid. This is so I can see what would be the biggest amount of gas released and then decide what sized measuring tube would give most accurate results.
After the apparatus was collected first I measured out 4g of marble chips and 25ml of pure acid. I then followed the method but instead of recording the gas at 10 second intervals I recorded at the end of 60 seconds. The experiment would then be repeated using the same concentration of acid to make sure my results were fair. I can then find out the most suitable measuring cylinder for the investigation.
The results I gathered from the preliminary experiment are below:
I decided to use a 250ml measuring cylinder because a 100ml measuring cylinder would be too small and a 250ml cylinder is the next size up.
Results
Conclusion
The results tell me that my prediction was correct; the stronger the concentration of acid the more gas there will be given off. This is explained because when the acid solution is poured onto the marble chips a reaction takes place. The acid solution makes the marble atoms vibrate faster as a solid and when the atoms are vibrating fast enough they are released as a gas. The gas, which is released from the marble chips, is carbon dioxide.
The formula for the chemical reaction is:
Ca CO³ + H CL = Ca CL
When the acid is poured onto the marble chips the chemicals combine together which releases the carbon dioxide. The graph shows a substantial difference between the different concentrations of acid. I noticed when observing the experiment that gas was not released straight away even though a react was obviously taking place; I think this is because pressure needed to build up in the conical flask to force the gas through the tube and into the beaker. I noticed that the stronger the concentration of acid the quicker the bubbles were released and the weaker the concentration the slower the bubbles were released.
Evaluation
I performed the test fairly by controlling all the variables except concentration of acid. The only slightly unfair factor was that even thought the marble chips were of a similar size they were not always of the same mass and surface area although I tried to get them roughly the same size.
I think that my results were reliable enough to draw a firm conclusion because my results were consistent with the pattern and matched the prediction. The lines on the graph I made were fairly straight and there were no anomalous results. To make the results more accurate I would have to change the way the experiment was set up. The only problem I encountered, which was of little consequence to the final results, was that sometimes air would get trapped in the tube and would be released into the measuring tube adding up to 2ml of gas. This had little effect on the overall results but it did show when I did the experiment with just water as there was ‘seemingly’ a small reaction with the water which should not have happened over such a short period of time. I believe this was because air had got into the tube and emptied into the measuring tube.
If I was going to do the experiment more accurately I would use just a conical flask and the amount of gas given off could be measured by sitting the conical flask on a weighing scale of a high accuracy and measuring the weight of the gas that was given off over a period of time. This would mean there would be no tubes for air to get trapped in.
